Waggin' Train chicken jerky tenders, sold by Nestle Purina Pet Care, are among top brands of Chinese-made pet treats linked to illnesses and deaths in U.S. dogs.

Newly posted results of more than five years of testing chicken jerky pet treats made in China appear to confirm assertions from government officials that they don’t know what’s making America’s dogs sick, even as complaints about the products have nearly doubled.

Federal Food and Drug Administration officials unexpectedly posted summaries this week of lab results of nearly 300 jerky treat samples collected and tested in the U.S. between April 2007 and June 2012. To see the results, click here.

The documents indicate that FDA scientists at labs nationwide tested for bacterial contamination, for mold and for chemicals used in antifreeze, resins and plastics that can harm pets. They tested for heavy metals and for the melamine and melamine analogs detected in pet food that sickened thousands of animals in 2007.

At the same time, new FDA figures indicate that the number of complaints of animal illnesses and deaths blamed on the treats has risen to more than 1,800, according to Tamara Ward, an agency spokeswoman.

The lab results show a mere handful of adverse findings related to the popular Chinese-made treats. None of the reports rose to the level of needing regulatory action, such as a recall, the documents indicate.

“This does not represent ALL testing that has and is being conducted by FDA,” Ward said in an email. “Additional testing is currently being conducted through other avenues.”

The FDA released the data a day after NBCNews.com reported that the agency had refused to release results of February inspections of the Chinese plants that make the treats. The agency said releasing the information would violate rules protecting trade secrets and confidential commercial information and that it would interfere with enforcement proceedings. That data remains confidential.

Pet advocates critical of the FDA said that while they welcome the release of the domestic data, the results indicate that the agency is not looking hard enough for the source of the illnesses, including hundreds of reports of vomiting, diarrhea and kidney failure.

“When I scanned down through the list of testing, they all seemed to be centered around the same handful of tests,” said Susan Thixton, who writes the blog TruthaboutPetFood.com. She believes the FDA needs to broaden its view to include other potential toxins.

"You can't find what you don't look for," she said.

FDA covered bases, experts sayBut animal health experts not affiliated with the FDA said the agency appears to be using due diligence to track the source of the problem. Tina Wismer, medical director of the ASPCA Animal Poison Control Center, said the review appears to be complete.

“Looking at what they’re testing for, I’m looking at the list of poisons that we know affect the kidneys and they’ve got their bases covered,” she said.

That’s a view echoed by Marion Ehrich, a professor of pharmacology and toxicology at the Virginia-Maryland College of Veterinary Medicine.

“From the website provided, it seems analyses of submitted samples have not yet led to the discovery of anything toxic that is consistently present in the samples,” she wrote in an email. “They have been looking at possible suspects (melamine, bacteria, molds, etc.) but nothing is standing out.”

The FDA is working to develop and validate new ways to detect toxic substances for which there are no current tests, said Ward, the agency spokeswoman.

The 284 samples included in the new data were collected after consumer complaints, as part of routine surveillance or as an assignment, Ward said. Of those, only six indicated adverse findings.

Those included salmonella found in three samples, including Dingo and Waggin Train chicken jerky products and in one unidentified product. Mold was found in a sample of Waggin’ Train jerky, too. Low levels of melamine were detected in one sample of Del Monte beef flavor jerky treats, the tests showed. Another Dingo treat had a questionable genetic fingerprint that was sent for further analysis.

In addition, a few samples were positive for undeclared propylene glycol, but not at levels that would have prompted regulatory actions, the documents said.

Most of the tests were like one posted on Aug. 20, 2007 for Waggin’ Train chicken jerky tenders. No melamine or related compounds including ammeline, ammelide or cyanuric acid was found, the test showed. No ethylene glycol or diethylene glycol -- toxic components of antifreeze -- were found.

The FDA has issued three warnings about jerky treats since 2007, including the most recent one last November. That’s a fairly strong action for an agency that typically keeps mum on investigations, said Kimberly May, a veterinarian and assistant director in the communications division for the American Veterinary Medical Association.

“This is as close as they’re going to come to saying there’s a problem,” May said. Officials with Nestle Purina Pet Care Co. and Del Monte Foods, which make the top brands of treats, insist that their products continue to be safe to feed animals as directed on the packages.

But some experts say it’s up to pet owners to be cautious.

“At this point in time, until we figure out exactly what is going on, I probably wouldn’t feed these,” the ASPCA's Wismer said.

A grieving pet owner says his 9-year-old dog was in perfect health until he fed her Waggin' Train chicken treats; the Pomeranian died 13 days later of kidney failure. He is now calling on the FDA to take another look at the product. WMAQ-TV's Michelle Relerford reports.